The invention relates to a parallel interface for connecting data processing devices to one another or to peripheral devices, particularly a personal computer to a printer, having at least two status information lines, disconnectable line drivers and control lines, the beginning of the data transmission being signaled by the transmitting device on a first control line for a predetermined data transmission direction and the end of the data transmission being signaled by the receiving device on a second control line.
To connect peripheral devices at a personal computer, a serial interface for data communication and a parallel interface for connecting a printer is provided, as a rule. The serial interface can be simultaneously used both for outputting and for inputting but is restricted in its speed to about 2 kBytes/s since the data is transmitted bit by bit. The parallel interface can reach an output speed of about 100 kBytes/s due to eight data lines which can be used in parallel and additional control lines. However, input from the peripheral device to the computer is not possible, it is only possible to transmit elementary status information items by means of dedicated signal lines, namely ready status ("selected"), end of paper ("paper end") and error ("error").
Today, printers are equipped with their own processors and can send back extensive test, diagnostic and status information when they are operated via a suitable interface. This particularly applies to printers in which the information to be printed is coded via the page description language of POSTSCRIPTTM in which this return information is expressly included in the language. For this purpose, such printers previously had to be connected via the serial interface. Although it is possible to omit the return channel in many cases in order to be able to utilize the higher speed of the parallel interface, cases are known in which a return channel cannot be omitted and thus the parallel interface cannot be used, for example a savings book printer which, before printing, must read a magnetic coding of the savings book from the savings book to be printed and transmit this coding back to the data processing device. Fast parallel and bidirectionally interfaces are also known. However, they are frequently not used because of the high additional costs for hardware and software required for them.